BOSTON (AP)  As another beach season draws to a close on Cape Cod, researchers are trying to figure out what”s driving the increase in shark sightings and encounters  including the state”s first attack on a human since 2012.

One prominent researcher suggests the presence of younger and smaller great white sharks this summer could be playing a role.

Greg Skomal, a state marine biologist leading a five-year study wrapping up this year, says his team spotted 149 great whites off Cape Cod in July, more than double the 74 observed last July and the 120 in 2016.

He said somewhat smaller great whites  measuring about 8 to 10 feet  appeared to make up a greater number of the sharks observed than in year”s past, though he said his team is still analyzing the data.

Skomal suggested more younger sharks could be contributing to the encounters that are increasingly being captured in viral photos and videos, particularly those of sharks snatching fish off anglers” hooks.

The waters between Cape Cod and New Jersey have been long been considered a regional white shark “nursery” where great whites spend the first years of their life before gradually expanding their territorial reach.

But more frequent spottings of juvenile sharks could suggest a broader recovery for Atlantic white shark populations, a phenomenon that”s already been documented on the U.S. west coast, said George Burgess, director emeritus of the International Shark Attack File, a database maintained at the Florida Museum of Natural History in Gainesville.

“If anything, it”s indicative of a healthy population,” Skomal said. “As the white shark rebounds across the East Coast, we should be seeing a broader range of sizes.”

Juvenile sharks could also simply be following their favored prey as they move into areas they”re not typically found, said Tobey Curtis, a shark researcher at the National Marine Fisheries Service in Gloucester, Massachusetts. The sharks tend to feast on bluefish, menhaden, dogfish and skates.

Climate change and the warming of the Cape”s waters sooner than usual could be another factor, said Robert Hueter, a shark expert at Mote Marine Laboratory and Aquarium in Florida.

“There”s no question that water temperature plays a huge role in where white sharks are found,” he said. “If the temperature in the ocean is changing, we could see them moving into places we wouldn”t expect.”

Cape Cod authorities, meanwhile, say they”re concerned about the safety of beachgoers  not just during the busy Labor Day weekend, but also the days beyond, when lifeguards stand down.

Officials say they”ve had to close beaches more frequently this year because of shark sightings. The National Park Service, which manages many of the picturesque beaches where white sharks tend to congregate, closed beaches for at least an hour about 25 times this year  more than double the annual average, said Leslie Reynolds, chief ranger for the Cape Cod National Seashore.

Local officials have also been stepping up public education efforts, but fear many beachgoers still aren”t heeding the warnings.

“The challenge is trying to convey the gravity of the situation to beachgoers,” said Nathan Sears, harbormaster in the town of Orleans. “Regardless of how much signage and information we provide, there still seems to be a concerning level of complacency.”

The heightened concern comes after a 61-year-old New York resident escaped a shark attack off Truro, Massachusetts with severe injuries to his leg and arm earlier this month.

Researchers are still working to determine what kind of shark was involved in the attack, but survivor William Lytton said, in hindsight, he took an “unnecessary risk” by swimming alone in fairly deep water, even if he was only about 10 feet from shore by his estimate.

He urged Labor Day beachgoers not to make the same mistake.

“Maybe,” Lytton suggested, “just stay in waist-high water.”

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Follow Philip Marcelo at twitter.com/philmarcelo. His work can be found at https://www.apnews.com/search/philip_marcelo.